Automotive glazing panel with solar control coating comprising a data transmission window

ABSTRACT

An automotive glazing panel has an electrically heatable solar control coating layer, spaced first and second bus bars positioned respectively adjacent a first and a second side edge of the glazing panel and adapted to relay electrical power to the coating layer and a data transmission window positioned adjacent the top edge of the glazing. This arrangement may be used to alleviate or reduce perturbations to heating of the glazing panel caused by the presence of the data transmission window.

This application is the U.S. national stage of International ApplicationNo. PCT/EP00/04199 filed May 1, 2000 which claims priority from EuropeanPatent Application No. 99201566.9 filed May 20, 1999. The entirety ofeach of those applications is incorporated herein by reference.

BACKGROUND OF THE INVENTION

This invention relates to glazing panels and particularly but notexclusively to vehicle windscreens provided with electrically heatablecoating stacks.

Whilst the primary role of a vehicle windscreen is to permit goodvisibility for a driver, various additional features may be incorporatedinto its design. Sensors or emitters arranged inside the vehicle mayrely on electromagnetic data transmission through the windscreen. Forexample, passage of an electromagnetic data signal for automatic paymentat the toll barriers used on the French motorway system may pass throughthe windscreen. It is also known to provide a window in the band ofblack enamel around the periphery of the windscreen, usually along thebottom edge of the windscreen, through which a vehicle identificationnumber or chassis number, often in the form of a bar code, can be readfrom the outside of the vehicle.

U.S. Pat. No. 4,668,270 (Ford Motor Company) describes a car windscreenhaving an electrically heatable coating layer used for defrosting,de-iceing and/or de-misting. The heatable coating, which is laminatedbetween the two glass sheets of the windscreen, is supplied withelectrical power via first and second bus bars which extend respectivelyalong the top and bottom edges of the windscreen, each bus bar beingsilk screen printed on the glass in a silver ceramic material. Theheatable coating is a multilayer coating consisting of layers of zincoxide and silver formed by magnetron sputtering.

Coating layers are well know not only to provide an electricallyheatable element but also to modify the optical properties of the glass,particularly to reduce the proportion of incident solar energy which istransmitted through the glass whilst allowing passage of sufficientvisible light to ensure good visibility. This can reduce overheating ofthe interior of the vehicle in summer and is commonly achieved byreflection of incident solar radiation in the infra-red portion of thespectrum. EP378917A (Nippon Sheet Glass Co.) discloses such coatinglayers. The term solar control coating layer as used herein refers to acoating layer which increases the selectivity of the glazing panel i.e.the ratio of the proportion of incident visible radiation transmittedthrough the glazing to the proportion of incident solar energytransmitted through the glazing. Many solar control coating layers havethe intrinsic property of being electrically heatable.

When a solar control coating is provided on a windscreen it isadvantageous for the solar control coating to cover the entire lighttransmitting portion of the windscreen so as to reflect as much of theincident solar energy as possible. A data transmission window in theform of a gap or hole may be provided in a solar reflecting coatinglayer specifically to allow the passage of electromagnetic waves throughthat portion of the glazing, for example to a sensor or emitter. Oneexample of this, as referred to above, is to allow passage of anelectromagnetic data signal for automatic payment at the toll barriersused on the French motorway system. The principle is neverthelessapplicable to allowing passage of any electromagnetic data transmissionsignal through a glazing panel, particularly using infra-redwavelengths. The term data transmission window as used herein refers toa portion of the surface area of a glazing adapted to permitelectromagnetic data transmission therethrough.

SUMMARY OF THE INVENTION

The invention allows a heatable solar control coating layer to becombined with a data transmission window in a particularly advantageousway.

The data transmission window may be substantially a four-sided polygon.Preferably, the data transmission window is not electrically coupled toan electrical element.

In one form, the data transmission window may have at least three sidessurrounded by the solar control coating layer.

For aesthetic reasons and so as not to impair the driver's vision thebus bars of a heatable coating layer of a car windscreen are usuallyarranged out of view. It has been common practice for bus bars to bearranged along the top and bottom edges (i.e. the longer two edges of acar windscreen) hidden from the inside of the car by the dashboard andthe interior bodywork and hidden from the outside by a band of blackenamel (which may have the additional role of blocking solar radiationto prevent deterioration of underlying glue securing the windscreen tothe car bodywork). This arrangement has been used to provide a suitabledistance and thus an appropriate electrical resistance between the busbars so as to allow a suitable electrical power to be dissipated in thecoating layer to provide the desired heating effect.

Data transmission windows in solar energy reflecting windscreens havegenerally been arranged towards the top edge of the windscreen, roughlycentrally between the two side edges. This may facilitate orientationand positioning of data transmitting and/or receiving instruments.

The inventors have appreciated that simply combining these two knowntechniques is undesirable as positioning of the data transmission windowin close proximity to the upper bus bar results in a significant gap ornon-conducting portion adjacent to the bus bar and increased risk ofprovoking uneven heating and undesirable hot spots in the coating layer.

This problem may be resolved by the invention without requiringrepositioning of the data transmission window or fundamental redesigningof either this or the bus bars.

The combination of the data transmission window with the bus barsarranged along the side edges of the windscreen may significantly reducethe perturbation to the flow of electrical current in the coating layercaused by the presence of the data transmission window.

In prior art arrangements having a substantially horizontal bus bararranged along the top edge of a windscreen, this bus bar must either beconnected to an electrical supply by a connector at the top edge of thewindscreen or the bus bar must be brought down one side of thewindscreen (avoiding contact with the electrically conducting coatinglayer) so as to allow arrangement of an electrical connector at thebottom edge of the windscreen. Arranging the bus bars adjacent to theside edges of the glazing may help to avoid this problem by allowing forconnection at or adjacent to the bottom edge of the windscreen.

Arrangement of the data transmission window in an elongate form mayfacilitate positioning of data transmitting and/or receiving instrumentsand passage of data signals. Arranging the elongation along the top orbottom edge of the glazing panel in combination with the defined bus bararrangement enables a desired surface area for the data transmissionwindow to be selected whilst reducing the width of the interruption inthe coating layer between the two bus bars. This may be used to minimisethe perturbation of current flow in the coating layer when electricallyheated.

The data transmission window preferably has a width comprised between 50mm and 100 mm, and a length comprised between 80 mm and 210 mm.

The data transmission window may have a width of at least 50 mm, 60 mm,70 mm, 80 mm, 90 mm or 100 mm. It may have a width of less than 300 mm,250 mm, 200 mm, 150 mm or 100 mm.

The data transmission window may have a length of at least 80 mm, 100mm, 120 mm, 140 mm, 160 mm, 180 mm or 210 mm. It may have a length ofless than 400 mm, 350 mm, 300 mm, 250 mm or 210 mm.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is an expanded schematic view of a car windscreen; and

FIG. 2 is an expanded schematic view of a car windscreen.

DETAILED DESCRIPTION

An embodiment of the invention will now be described, by way of exampleonly, with reference to FIG. 1 and FIG. 2, both of which are expandedschematic views of a car windscreen.

Windscreen 10 illustrated in FIG. 1 comprises an inner sheet of glass 11laminated to an outer sheet of glass 13 by means of a sheet of pvb 12.

The windscreen is substantially trapezial in shape having a top edge 21,a longer bottom edge 23 substantially parallel thereto and side edges22, 24. The windscreen has a spherical, curved configuration so that itis curved both along an axis parallel to the top edge 21 and along anaxis perpendicular to the top edge 21 (for ease of representation thecurvature of the windscreen is not shown).

An electrically conducting solar control layer 25 is positioned betweenthe inner and outer sheets of glass 11, 13. Typically this is amulti-layer coating having the general configuration antireflectivedielectric layer/silver containing layer/antireflective dielectriclayer/silver containing layer/antireflective dielectric layer depositedby sputtering. The coating layer may be carried for example on the innerface of the outer-sheet of glass 13 (i.e. face 2) or on a supportingfilm, for example of PET.

The coating layer 25 is spaced from the external periphery of thewindscreen by a non-conducting peripheral band (not shown) provided inthis example by a band in which the coating layer has either not beendeposited or has been removed. This prevents the electrically conductivecoating extending to the very edge of the windscreen and may also reducethe risk of corrosion of the coating layer.

A data transmission window 27 is provided as part of the glazing panelwithin the coating layer. In the example of FIG. 1, the datatransmission window 27 is partially surrounded by the coating layer 25but in other embodiments it may be entirely surrounded. The datatransmission window may be formed by removing a portion of the coatinglayer or by masking when the coating layer is deposited.

Electrical power is supplied to the coating layer via a first bus bar 31arranged in contact with the coating layer 25 adjacent to the first sideedge 22 of the windscreen and a second bus bar 32 arranged in contactwith the coating layer 25 adjacent to the second side edge 23 of thewindscreen. The bus bars may be formed in any suitable manner, forexample by silk screen printing of a conducting enamel materialunderneath or on top of the coating layer or by means of conducting tapeor conductive strips, for example conductive copper or tinned copperstrips. Connectors (not shown) for facilitating connection of the busbars to a car's electrical circuit may protrude from the glazing and maybe arranged adjacent to each other (not shown).

In FIG. 2, the data transmission window 27 is entirely surrounded by thecoating layer 25.

Each of these arrangements may be used to allow the coating layer tocover at least the majority of the light transmitting surface of thewindscreen without provoking significant perturbation in the heatingarrangement of the coating layer.

Whilst the invention has been particularly described in relation to awindscreen it will be understood that it is applicable to otherautomotive glazing panels, for example, side windows, rear windows andsunroofs.

1. An automotive windscreen glazing panel in which the glazing panel perimeter comprises at least a top edge, a bottom edge and first and second side edges, the bottom edge being longer than the top edge and substantially parallel thereto and each of the side edges being substantially the same length as each other and shorter than the top edge, in which the glazing panel is provided with an electrically heatable solar control coating layer over at least part of its surface area, in which the glazing panel is provided with a data transmission window adapted to permit electromagnetic data transmission therethrough, in which the data transmission window permits transmission of a greater proportion of incident electromagnetic data than the proportion of incident electromagnetic data transmitted by an equivalently sized portion of the glazing panel provided with the solar control coating, in which the data transmission window is at least in part surrounded by the coating layer and is positioned adjacent to either the top edge or the bottom edge of the glazing panel, in which the first bus bar is arranged substantially adjacent to and extends substantially along the first side edge of the glazing panel, and in which the second bus bar is arranged substantially adjacent to and extends substantially along the second side edge of the glazing panel, in which the arrangement of the solar control coating, the bus bars and the data transmission window is such as to allow the coating layer to cover at least the majority of the light transmitting surface of the windscreen without provoking significant perturbation in the heating arrangement of the coating layer.
 2. The automotive glazing panel in accordance with claim 1, the glazing panel having one of the following: (a) the data transmission window is positioned adjacent the top edge of the glazing panel; (b) the data transmission window is positioned adjacent the bottom edge of the glazing panel.
 3. The automotive glazing panel in accordance with claim 2 and further including at least one of the following: (c) the data transmission window is substantially elongate in shape with its elongation stretching substantially parallel to the top edge of the glazing panel; (d) the data transmission window is substantially elongate in shape with its elongation stretching substantially parallel to the bottom edge of the glazing panel; (e) the data transmission window is at least partially surrounded by the coating layer; (f) the data transmission window is substantially surrounded by the coating layer; (g) the minimum distance between the periphery of the data transmission window and either of the first bus bar or second bus bar is at least 300 mm; (h) the data transmission window has a width which is at least 50 mm and which is less than 300 mm and a length which is at least 80 mm and which is less than 400 mm; (i) the data transmission window has a width comprised between 50 mm and 100 mm and a length comprised between 80 mm and 210 mm.
 4. A method of controlling heat dissipation over at least a part of the surface area of an automotive glazing panel comprising providing a glazing panel made in accordance with claim
 2. 5. A method in accordance with claim 4 in which the heat dissipation is controlled substantially evenly over a majority of the surface area of the glazing panel.
 6. A method of controlling heat dissipation over at least a part of the surface area of an automotive glazing panel comprising providing a glazing panel made in accordance with claim
 1. 7. A method in accordance with claim 6 in which the heat dissipation is controlled substantially evenly over a majority of the surface area of the glazing panel. 